1032.cpp

哈尔滨工业大学ACM 竞赛网上在线试题集锦的源代码

/*  This Code is Submitted by wywcgs for Problem 1032 on 2005-12-26 at 10:44:14 */ 
#include <cstdio>

const int MAX = 102400;

int main()
{
	double x[MAX], y[MAX];
	double A, Cx, Cy;
	int t, T, i, n;
	
	scanf("%d", &T);
	for(t = 0; t < T; t++) {
		scanf("%d", &n);
		for(i = 0; i < n; i++) {
			scanf("%lf %lf", &x[i], &y[i]);
		}
		x[n] = x[0], y[n] = y[0];
		A = Cx = Cy = 0;
		for(i = 0; i < n; i++) {
			double p = x[i]*y[i+1] - x[i+1]*y[i];
			A += p;
			Cx += (x[i]+x[i+1]) * p;
			Cy += (y[i]+y[i+1]) * p;
		}
		printf("%.2lf %.2lf\n", Cx/(3*A), Cy/(3*A));
	}
	
	return 0;
}